Closed-loop Hall effect current transformers (CT) have been used and known for several years. For example, see U.S. Pat. No. 3,573,616, incorporated herein by reference. An excellent type of such closed loop CT is one with a good signal to noise ratio, in other words having a high signal output. Such a CT device can be made with indium antimony (InSb), but indium antimony is characterized by having poor linearity and a very strong negative temperature coefficient regarding its main terminal resistance.